There is an increasing demand for a high data rate in wireless communications. As techniques that fulfill such a demand, techniques, such as SDM (Space Division Multiplexing), OFDM (Orthogonal Frequency Division Multiplexing), MLD (Maximum Likelihood Detection), polarization diversity, and adaptive phase control, have been proposed in the following documents.    [Non-patent document 1]A. V. Zelst, R. V Nee and G. Awater, Space Division Multiplexing (SDM) for OFDM Systems, Proc. of VTC, pp. 15-18, 2000.    [Non-patent document 2]P. Vandenameele, L. V. Perre, M. G. E. Engels, B. Gyselinck and H. D. Man, A combined OFDM/SDMA approach, IEEE Journal of sel Area in Common, vol. 18, no. 11, pp. 2312-2321, 2000.    [Non-patent document 3]J. J. A. Lempianen, J. K. Laiho-Steffens, A. Wacker, Experimental results of cross polarization discrimination and signal correction values for a polarization diversity scheme, Proc. of VTC 97, vol. 3, pp. 1498-1502, 1997.    [Non-patent document 4]T. Kambayashi, T. Horinouchi, M. Shibahara, T. Fujii and I.
Sasae, SDM/OFDM system using adaptive transmit phase control to mitigate co-channel interference, Proc. of VTOC 02 fall, pp. 2091-2095, 2002.
Non-patent document 1 discloses an invention which combines the OFDM scheme with the SDM scheme. Particularly, it shows that the use of a plurality of antennas on both a receiver side and a transmitter side can achieve a high transfer rate on multiple input multiple output (MIMO) channels.
In the OFDM/SDM scheme, however, various schemes which can achieve faster communications with higher quality are further demanded.
Non-patent document2 discloses an MLD scheme. It is known that the SDM scheme degrades the transfer quality due to co-channel interference (CCI). While schemes to mitigate co-channel interference include MMSE (Minimum Mean Square Error), PIC (Parallel Interference Canceler), and SIC (Serial Interference Canceler), MLD has the best performance among them. Particularly, a scheme of separating a desired signal and a CCI signal by generating a replica of a received signal and using a pilot signal is disclosed.
It is known however that when the reception powers of desired symbols received from different antennas are close to each other, the same replica is generated, thus degrading the MLD detection performance.
Further, non-patent document 3 discloses a polarization diversity scheme. It is known the XPD (CROSS Polarization discrimination) value for a combination of a horizontal polarization antenna and a vertical polarization antenna varies between 5 dB and 15 dB depending on the environment.
This is the result of measuring the ratio of reception powers in orthogonal diversity branches. When the reception powers of the polarization branches become equal to each other, the maximum diversity gain is achieved.
When the unbalance of reception powers becomes large, however, the entire diversity system will not operate. This is because weak channels are neglected at the stage of coupling diversities.
Non-patent document 4 discloses an adaptive phase control scheme in SDM/OFDM communication. In particular, a system which requires a look-up table and feedback information for adaptively controlling the phase is disclosed.
In consideration of a case where the amplification factors become identical and the phases become identical, the look-up table and feedback information should be made huge.
The invention has been made to solve various problems of the known systems, and it is an object of the invention to provide a communication system, a transmitter, a receiver, a transmitting method, and a receiving method, which efficiently perform communications using antennas of different polarizations, and a program which allows a computer to realize them.